1. Field of the Invention
The present invention relates generally to a mechanical seal device which not only is economical in manufacture cost and assembly cost of parts thereof but also prevents squealing noises and wear of sliding surfaces thereof. More particularly, the invention relates to a mechanical seal device in which a certain arrangement of the assembly parts thereof materializes prevention of squealing and wear at the seal surface of a seal ring during relative sliding movement as well as improvement of durability of a gasket supporting the seal ring.
2. Description of the Related Art
A seal ring to provide a seal against a sealed fluid, in general, is made of a hard material such as silicon carbide in order to prevent wear of seal surface thereof. A gasket being made of a rubber-like elastic material is typically employed in order to effect a seal at the installation surface wherein the seal ring is retained as well as to provide a support for the seal ring. The support provided by the gaskets however, suffers from a torsional deformation to circumferential direction thereof which is caused by a rotary torque acted on the seal surface. Although the seal ring is fixed by means of a support portion of a retainer ring in order to circumvent the torsional deformation, engagement arrangement between the retainer ring and the seal ring becomes complicated because the seal ring needs to fixate engagement portion thereof with the retainer ring while simultaneously being fitted to the gasket. Such a complex arrangement in the engagement arrangement causes various difficulties against the gasket as well as the seal surface of the seal ring.
FIG. 4 displays a mechanical seal device 211 as a first prior art related to the present invention. The figure shows a half portion of a cross-sectional view of the mechanical seal device 211. In FIG. 4, a rotary seal ring 202 having a seal surface 202A is fitted at inner circumferential surface thereof with a cup gasket 204. The cup gasket 204 then is fitted with a mount portion 203D of a sleeve member 203. Outer circumferential surface of the rotary seal ring 202 disposes two or four equally spaced slot portions 202G, and each slot portion 202G forms an engagement flat surface 202T at the bottom of the slot. The mount portion 203D disposes a holding plate 203A which protrudes therefrom. The holding plate 203A is inserted into the slot portion 202G with a play against the side walls of the slot portion 202G. One rotary seal portion 201 in which the rotary seal ring 202 is fitted with the cup gasket 204 and the cup gasket 204 then is mounted onto the sleeve member 203 is arranged such that a fixing portion 203C of the rotary seal portion 201 can be fittingly fixed to a rotary shaft at inner diameter surface thereof.
Stationary seal ring 212, on the other hand, is fittingly fixed with a bellows member 214. Outer diameter portions of both distal end portions of the bellows member 214 fittingly mate with a first retainer portion 213A and a second retainer portion 213B, respectively, which effectively anchor the bellows member 214 at distal end portions thereof. A cartridge member 215 is fixed to a housing at one end thereof while other end thereof is fitted with the inner diameter surface of the stationary seal ring 212 in a slidable manner. In addition, a coil spring 219 is disposed between the first retainer portion 213A and the cartridge member 215. The spring 219 resiliently urges the stationary seal ring 212 against the rotary seal ring 202. This effects a seal against the sealed fluid by bringing an opposing seal surface 212A of the stationary seal ring 212 into seal-tight contact with the seal surface 202A of the rotary seal ring 202.
As illustrated in FIG. 4 and FIG. 5 including the aforementioned arrangement, a plurality of holding plates 203A which are disposed at the outer perimeter of the mount portions 203D are inserted into the respective slot portions 202G which are formed at the outer circumference of the rotary seal ring 202. It, however, is very difficult to make the width B of the holding plate 203A same as the width A of the mating slot portion 202G under current fabrication technologies due to presence of machining tolerance. Even if it is assumed that the width A and width B have exactly the same dimension, there remains another problem in that it is almost impossible to exactly align the locations of a plurality of holding plates 203A with those of the corresponding slot portions 202G which are spaced apart along the circumference. Therefore the width B of the holding plate 203A needs to be made smaller than the width A of the slot portion 202G so that the holding plate 203A leaves a gap to sides thereof for an easy installation. With such an arrangement, the holding plates 203A can be fitted to respective slot portions 202G. Furthermore, the rotary seal ring 202 is fixedly retained by the cup gasket 204 which is elastically deformable. When the seal surface 202A of the rotary seal ring 202 is subjected to a sliding movement relative to the opposing seal surface 212A of the stationary seal ring 212, a frictional force during the sliding movement generates a torque which will in turn induce a reciprocal torsion to the cup gasket 204 which connects the sleeve member 203 and the rotary seal ring 202 because of the clearance between the holding plate 203A and the slot portion 202G. This forces the seal surface 202A to repeat a stick-and-slip motion during the operation, which causes squealing noises at the relatively sliding seal surfaces 202A, 212A. To make things worse, the squealing and abnormal slip motion will lead to a rapid wear of the relatively sliding seal surfaces 202A, 212A and the cup gasket 204 will not last long as expected due to the reciprocal torque load. As a result, the mechanical seal device 211 will lose seal ability and durability thereof.
There is another mechanical seal device 111 shown in FIG. 6 as a second prior art relative to the present invention. Gross arrangement of the mechanical seal device 111 is more or less similar to that in FIG. 4, hence not shown. The overall arrangement will be described according to FIG. 6 and FIG. 5. What makes the mechanical seal device 111 in FIG. 6 different from the mechanical seal device 211 in FIG. 5 resides in a seal ring 102 and a sleeve's mount portion 103D, which will be explained in detail by using FIG. 6. As shown in FIG. 6, the rotary seal ring 102 forms a pair of engagement flat surfaces 102B, 102B at two symmetrical locations, top and bottom, of the outer perimeter surface. And the inner circumferential surface of the rotary seal ring 102 is fitted to the outer diameter surface of an annular cup gasket 104. The cup gasket 104 serves as a joint member to fittingly fixate the rotary seal ring 102 to an annular mount portion 103D of the sleeve. FIG. 6 also shows that the mount portion 103D retains a pair of flat holding plates 103A, 103A formed on the outer perimeter of the sleeve. The holding plates 103A, 103A are arranged in such a manner that the plates are kept in close contact state with the engagement flat surfaces 102B, 102B of the seal ring 102.
Arrangement of opposing members relative to the rotary seal ring 102 is omitted in FIG. 6, thus referring to FIG. 4. Disposed in opposite to the rotary seal ring 102, as shown in FIG. 4, is a stationary seal ring 212. The stationary seal ring 212 comes into contact with a bellows member 214 which is disposed between the stationary seal ring 212 and a cartridge member 215 which is connected with the housing. One end portion of the bellows member 214 is urged by a spring 219. An opposing seal surface 212A of the stationary seal ring 212 which is thus urged by the spring 219 via the one end portion of the bellows member 214 is brought into seal-tight contact with the seal surface 102A of the rotary seal ring 102 shown in FIG. 6.
The way the device in FIG. 4 and FIG. 6 operates is hereafter similar to one another. Therefore problems encountered in FIG. 6 will be dealt with by referring to FIG. 4. It is noted that parenthesized numerals correspond to those of FIG. 6. The mechanical seal device 211 (111) effects a seal against a sealed fluid within the apparatus by bringing the opposing seal surface 212A of the stationary seal ring 212 into seal-tight contact with the seal surface 202A of the rotary seal ring 202(102) as the result of the stationary seal ring 212 being urged by the spring 219 via the bellows member 214. The sleeve member 203 is fittingly fixed with the rotary shaft in order to rotate together. Then the rotary seal ring 202(102) which is mounted to the mount portion 203D(103D) via the cup gasket 214(104) is forced to rotate together with the rotary shaft after the engagement flat surface (102B) engages the holding plate (103A). However, bringing the engagement flat surface (102B) into seal-tight contact with the holding plate (103A) is very difficult to achieve from the machining point of view, because it requires that the cup gasket 214(104) be fitted not only with the mount portion 203D(103D) but also with the rotary seal ring 202(102). Also the holding plate (103A) needs to be directly worked to obtain the annular mount portion 203D(103D) by a press forming method, which will inevitably restrict machining accuracy. In addition, pressing the holding plate (103A) too much against the engagement flat surface (102B) causes unwanted strains to the seal surface 202A.
As shown in FIG. 6, pressing a pair of the symmetrically arranged engagement flat surfaces (102B) of the rotary seal ring (102) causes deformation of the seal surface 202A. Therefore a certain clearance is disposed between the engagement flat surface (102B) and the holding plate (103A). The seal surface 202A and the opposing seal surface 212A repeat a sticking and a relative sliding motion one after the other because of elastic torsional deformation of the cup gasket 204(104) in the circumferential direction and the clearance gap existing between the width dimension B of the engagement flat surface 102B and the width dimension A of the holding plate 103A. The repeated sticking and relative sliding motion causes a squealing noise. The sticking further accelerates wear in the seal surface 202A. As the result, the seal ability of the mechanical seal device 211(111) will decrease.
The present invention is introduced to resolve the above mentioned problems. A primary technical goal which this invention tries to achieve is to make part machining and assembly of a mechanical seal device straightforward and to improve durability of a gasket supporting a seal ring by protecting the gasket from torsional fatigue. Another goal is to prevent squealing noises of a seal surface during sliding movement thereof and to reduce wear of the seal surface.